The reason Dryden chose to recast the story of Antony and Cleopatra after Shakespeare and others had done so is explained in his own words in the Dedication to his drama. The reasons he gives are three. (1) Since many had done so already and had done so so "variously," he was given "confidence to try" his own effort. (2) His motive was what he believed the motives of his predecessors had been: to give a good and important moral. (3) He drew Antony and Cleopatra "favorably" so they might elicit pity even while their lack of virtue is revealed, the end goal being demonstrating that "our passions ... ought to be within our power." In short, Dryden wanted to present a time honored tale of the "unfortunate" results of failing to live a virtuous life.
The death of Antony and Cleopatra is a subject which has been treated by the greatest wits of our nation, ... that their example has given me the confidence to try myself .... I doubt not but the same motive has prevailed with all of us in this attempt; I mean the excellency of the moral: For the chief persons represented were famous patterns of unlawful love; and their end accordingly was unfortunate. ... I have ... drawn the character[s] ... as favourably as Plutarch, Appian, and Dion Cassius would give me leave ... for the crimes of love, which they both committed, were not occasioned by any necessity, or fatal ignorance, but were wholly voluntary; since our passions are, or ought to be, within our power. (Dedication, Dryden)
This leads into the question of the play's significance as a Restoration play. The Restoration is the period in English history following the death of the Puritan Cromwell. He had formerly put King Charles I to death and taken the throne away from the monarchy. Thereafter he ruled England as a Protestant republic. Dryden dedicates All for Love to the restored King of England, King Charles II, who had been restored as King to the restored monarchy of England. Any plays written during this historical period are identified by the period of time and called Restoration plays.
There are a couple of points of significance related to Dryden's play. One of the most notable is that, after having written what are referred to as Restoration "bombastic" heroic plays versed with couplets, e.g., Conquest of Granada, Dryden combined the heroic play with tragedies in the French style of Racine (Gary R. Young) to (1) reduce the bombast (i.e., inflated and pretentious style) and (2) replace the couplets with blank verse. Dryden thus significantly introduced a new tone and style into English drama. In addition, All for Love is significantly counted as one of Dryden's greatest dramatic works.